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Physics

Physics. Mr. Jongie G. Gepulgani. The Gas Laws. This topic will focus on the volume and density of gases under varying conditions of temperature and pressure. The Boyle’s Law. A decrease in volume produces an increase in absolute pressure. or. The Boyle’s Law. Sample problem:

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Physics

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  1. Physics Mr. Jongie G. Gepulgani

  2. The Gas Laws This topic will focus on the volume and density of gases under varying conditions of temperature and pressure.

  3. The Boyle’s Law • A decrease in volume produces an increase in absolute pressure. or

  4. The Boyle’s Law Sample problem: A cylinder fitted with a piston contains gas at a pressure of 35.5 lbs/in2 as indicated by a gage mounted to the outside of the cylinder. The atmospheric pressure is 14.5 lbs/in2 . If the piston is forced down reducing the volume in the cylinder to one-fourth of its original volume while holding the temperature of the gas constant, determine the new reading on the pressure gage.

  5. The Boyle’s Law The Solution: Get the absolute pressure: From the equation:

  6. The Boyle’s Law The Solution: Substitute values: Solving for P2: absolute Since we are asked for the gage pressure, then:

  7. The Charles’ Law The volume is directly proportional to the absolute temperature at constant pressure. The absolute temperatures can either be Kelvin degrees or Rankine degrees.

  8. The Charles’ Law Sample problem: A quantity of air occupies a volume of one cubic foot on a day when the temperature is 15 degrees F. What will be the volume of this quantity of air when the temperature increases to 85 degrees F, and the pressure stays the same?

  9. The Charles’ Law The solution: Convert degrees F to degrees R first. From the equation:

  10. The Charles’ Law Hence, Cross multiply:

  11. The Gay-Lussac’s Law An increase in the absolute temperature of the gas, the average speed of the molecules increases in constant volume. The faster the speed, the greater the pressure the gas molecules exert.

  12. The Gay-Lussac’s Law Sample problem: The tire of a bicycle is filled with air to a gage pressure of 50.0 lbs/in2 at 58 degrees F. What is the gage pressure in the tire on a day when the temperature rises to 86 degrees F? Assume that the volume of the tire does not change and the atmospheric pressure is 14.7 lbs/in2 ?

  13. The Gay-Lussac’s Law The solution: Convert first to absolute temperatures and pressures. Substituting these values to the formula:

  14. The Gay-Lussac’s Law But we need to convert the absolute pressure to gage pressure. Thus,

  15. Next topic : • The General Gas Law, The Atmosphere

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